eatinggrumble84 I don't think it's necessary to unintall the old version of Messages, to get the latest version working with the ICC toggle.
I was still on 20241120_00_RC07. I just updated to the latest Play Store version of Messages. Then as an experiment, I waited to see how long that would work, because some people said they were no longer having the 36 hour reset with the latest version, after getting connected with an old version. I was just curious. In my case, by 6 hours RCS failed.
So then I went and enabled the ICC toggle, went back to Messages which was now stuck at "connecting," disabled RCS, reenabled it and it was still stuck. Then I rebooted and it connected and RCS was working immediately. Unfortunately, for me the Play Store version of Messages does not show the RCS Connection State option in the debug menu, so I can't verify the status of Etouffee (a lot of people seem to have this experience with newer versions of Messages). So I have to just go by whether individual threads show as RCS or not. But in any case, I've now sent and received RCS messages without issue.
I haven't yet used adb to set READ_DEVICE_IDENTIFIERS back to deny for Play Services, because I've been traveling and have not had time. But according to @inthewaves it shouldn't matter and for newer versions of Messages isn't doing anything (Play sevices gets the permission anyway when newer versions of Messages are set as the default SMS app--whereas 20241120_00_RC07 was too old and excluded from this).
But back to RCS and the ICC toggle. I do wonder if I even rebooting was necessary. Maybe toggling airplane mode would have done the same thing, but I didn't think of trying that.
Anyway, I think people should keep it simple. Just update to the Play Store version of Messages, make sure it's set as the default SMS app, enable the ICC toggle and follow the directions in the pop up about permissions, and then if necessary reboot (or try toggling airplane mode first).
A lot of people, "just to be on the safe side," or following some logic like that, are clearing caches, uninstalling Messages, before installing the latest version, and doing lots of other things, that make the whole process more complicated. Then when RCS works, other people are led to belive they need to do all these steps. I think it's better to start with the minimum number of steps and see if it works. Otherwise, we'll never narrow things down to what is actually necessary and what is extraneous.